Process for hydrogenating acetylenes

ABSTRACT

A process for selectively hydrogenating C4-acetylenes in a liquid hydrocarbon stream containing largely butadiene has been developed. Hydrogen and the hydrocarbon stream are contacted with a catalytic composite comprising an inorganic oxide support having dispersed thereon finely divided copper metal and an activator metal of nickel, cobalt, platinum, palladium, manganese, or a combination thereof where 1) the catalytic composite has an average diameter of up to about {fraction (1/32)} inch (800 microns) and/or 2) at least 70 weight percent of the copper metal and the activator metal are dispersed on the outer 200 micron layer of the support.

FIELD OF THE INVENTION

A process for the selective hydrogenation of C₄-acetylenes in thepresence of butadiene with the added benefit of extended catalyststability has been developed.

BACKGROUND OF THE INVENTION

Butadiene is an important starting material for the production of highmolecular weight polymers and is used extensively to form syntheticrubber including styrene-butadiene rubber, nitrile-butadiene rubber,buna-S rubber, and trans-polybutadiene rubber, and adiponitrile andstyrene butadiene latex in paints. Butadiene is usually a by-productfrom steam cracking naphtha. However, the product butadiene regularlycontains impurities that must be removed before the butadiene may beused as a starting material. The principal impurities are acetylenesincluding ethylacetylene, methylacetylene and vinylacetylene.Historically, two approaches have been used to remove the acetylenes:extractive distillation using a solvent to selectively absorb theacetylenes, or selective hydrogenation of the acetylenes.

In using selective hydrogenation, copper-containing catalytic compositeshave been shown to be successful. Copper-containing catalytic compositesused for selective hydrogenation of acetylenes are disclosed in U.S.Pat. No. 4,493,906 which discloses the catalyst as {fraction (1/16)}inch extrudates, U.S. Pat. No. 4,440,956 which discloses the catalystsas ⅛ inch pellets, U.S. Pat. No. 3,912,789, U.S. Pat. No. 3,218,268which disclose the catalysts as {fraction (3/16)} inch tablets, and U.S.Pat. No. 3,751,508 which disclose the catalysts as 3 mm tablets (about ⅛inch tablet). In contrast to this art, applicants have discovered that acopper-containing catalytic composite where. at least 70 weight percentof the copper and optionally one or more activator metals are dispersedon the outer 200 microns of the catalyst support. It is most preferredthat the catalyst composite particles also have an average diameter ofabout {fraction (1/32)} inch (800 microns) or less. A microspherecatalyst is shown herein to have much improved stability and selectivityversus similar catalysts having particles of about {fraction (1/16)}inch (1600 microns) diameter.

SUMMARY OF THE INVENTION

The present invention is related to a process for selectivelyhydrogenating C₄-acetylenes in a liquid hydrocarbon stream containinglargely butadiene with the benefit of increased catalyst stability.Hydrogen and the hydrocarbon stream are contacted with a catalyticcomposite comprising an inorganic oxide support having dispersed thereonfinely divided copper metal and optionally an activator metal selectedfrom the group consisting of nickel, cobalt, platinum, palladium,manganese, and a combination thereof where at least 70 weight percent ofthe copper metal and the activator metal are dispersed on the outer 200micron layer of the support. In a specific embodiment of the invention,at least 80 weight percent of the copper metal is dispersed on the outer200 micron layer of the support. In another specific embodiment of theinvention, hydrogen and the hydrocarbon stream are contacted with acatalytic composite comprising an inorganic oxide support havingdispersed thereon finely divided copper metal and optionally anactivator metal selected from the group consisting of nickel, cobalt,platinum, palladium, manganese wherein the catalytic composite isspherical and has an average diameter of about {fraction (1/32)} inch(800 microns) or less.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures contain the results of the accelerated stability experimentsconducted in Example 3. FIG. 1 shows the weight percent conversion ofvinyl acetylene over time when using a microspherical catalyst of thepresent invention as compared to three reference catalysts. FIG. 2 showsthe weight percent conversion of total acetylenes over time when using acatalyst of the present invention as compared to three referencecatalysts. FIG. 3 shows 1,3-butadiene retention over time when using acatalyst of the present invention as compared to three referencecatalysts. FIG. 4 shows weight percent hydrogen conversion over timewhen using a catalyst of the present invention as compared to threereference catalysts. FIG. 5. shows the hydrogen:acetylene usage ratio(moles hydrogen consumed divided by moles acetylenes consumed) over timewhen using the catalyst of the present invention as compared to threereference catalysts. FIG. 6 shows selectivity to polymeric byproductsover time when using the catalyst of the present invention as comparedto three reference catalysts.

DETAILED DESCRIPTION OF THE INVENTION

In general terms, the invention is a process for selectivelyhydrogenating C₄-acetylenes in the presence of large amounts ofbutadiene by contacting the hydrocarbons with a supported catalyticcomposite where at least 50 weight percent of the active catalyticagents, preferably at least 70 weight percent, more preferably at least80 weight percent, and most preferably at least 88 weight percent, arelocated on the outer 200 micron layer of the support. Another embodimentof the invention is one where the support is spherical and has anaverage diameter of less than about {fraction (1/32)} inch (800microns). The invention further reduces the production of undesired highmolecular weight polymerized byproducts thereby extending the stabilityand enhancing the selectivity of the catalyst. The term “C₄-acetylenes”as used herein is meant to include vinylacetylene, ethylacetylene, andmethylacetylene. The vinylacetylene is hydrogenated to 1,3-butadiene,the ethylacetylene is hydrogenated to 1-butene, and the methylacetyleneis hydrogenated to propylene.

The C₄-acetylenes are typically formed as a byproduct in butadieneproduction and must be removed before the butadiene can be furtherprocessed. The acetylenes are may be in a concentration ranging fromabout 0.5 to about 3 weight percent, or higher, of the product liquidhydrocarbon stream from a butadiene production reactor. The liquidhydrocarbon stream generally contains butadiene (40-50 weight percent),butenes (40-50 weight percent), butanes (5-10 weight percent) andC₄-acetylenes. Propane and C₃-acetylenes are also present in minorquantities. In a typical treating process, hydrogen and the hydrocarbonstream are introduced to a fixed bed reactor. Various methods ofintroducing hydrogen to the reactor are known and any such method issuitable for use in this invention. The preferred method is to admix thehydrocarbon stream with a stoichiometric amount of hydrogen and thenintroducing the mixture to a fixed bed reactor.

The fixed bed reactor contains a catalytic composite effective tocatalyze the selective hydrogenation of the acetylenes. The catalyticcomposite must be “selective” to the acetylenes so as to minimizehydrogenation of the desired butadiene. The catalytic composite containsfinely divided copper metal and one or more activator metals which arebound to a support. The activator metals are those which are normallyintroduced in the form of salts and whose oxides are reducible byhydrogen. Suitable activator metals include nickel, cobalt, manganese,platinum, palladium, or a combination thereof. The most preferredactivator metal is nickel. The copper is present in an amount rangingfrom about 5 to about 15 weight percent of the whole finished catalyticcomposite in the oxidized form and the activator metal is present in anamount ranging from about 0.1 to about 1 weight percent of the wholefinished catalytic composite in the oxidized form. Suitable methods ofdepositing the metals on the support are discussed below.

The support may be refractory inorganic oxide materials such as silica,alumina, carbon, titania, magnesia, zirconia, clays, zeolites, and acombination thereof. The aluminas which can be used as a support includegamma, theta, delta, and alpha alumina with gamma and theta aluminabeing preferred. The zeolites which can be used include faujasites,zeolite Beta, L-zeolite, ZSM-5, ZSM-8, ZSM-11, ZSM-12, and ZSM-35. Thepreferred refractory inorganic oxides are gamma and theta alumina.

The support may be of any suitable size and shape including sphericaland extruded supports. The extruded support is prepared as commonlyknown in the art.

The extrudate is preferably cylindrical with {fraction (1/32)} inchdiameter. The support may also be a shaped support such as a trilobe,quadrulobe, irregular shaped particles, pellets, or hollow tube whichpreferably posses a maximum diffusion path of {fraction (1/32)} inch orless. The support may also be spherical with typical sphere sizes usedin process such as these include {fraction (1/16)} inch and ⅛ inch. Apreferred spherical support is of a “microsphere” size, which includesspheres of support material nominally having a diameter of about{fraction (1/32)} inch (800 microns) or less. The spheres are preferablyproduced by commonly known oil-dropping techniques such as described inU.S. Pat. No. 2,620,314, which is incorporated by reference. The oildrop method comprises forming an aluminum hydrosol by any of thetechniques taught in the art and preferable by reacting aluminum metalwith hydrochloric acid; combining the hydrosol with a suitable gellingagent, e.g., hexamethylenetetramine; and dropping the resultant mixtureinto and oil bath maintained at elevated temperatures, The droplets ofthe mixture remain in the oil bath until they set and form hydrogelspheres. The spheres are then continuously withdrawn from the oil bathand typically subjected to specific aging and drying treatments in oiland ammoniacal solutions to further improve their physicalcharacteristics. The resulting aged gel spheres are then washed at about70° C. to about 100°C. and dried at a relatively low temperature ofabout 65° C. to about 260° C. then calcined at a temperature of about455° C. to about 705° C. for a period of about 1 to about 20 hours. Thistreatment effects conversion of the hydrogel to the correspondingcrystalline gamma-alumina. If theta alumina is desired then the hydrogelspheres are 20 calcined at a temperature of about 950° C. to about 1200°C.

While microspheres are preferred, a variety of support shapes aresuitable, as discussed above. It is preferred that the support, whetherspherical or not, have an effective diameter of about {fraction (1/32)}inch (800 microns) or less. For a non-spherical support, effectivediameter is defined as the diameter of the shaped article would have ifit were molded into a sphere.

The catalytic metal copper, and the activator metal(s) may be dispersedonto the support by means well known in the art such as impregnation,coprecipitation, cogellation or ion exchange. The preferred method ofincorporating the metal copper and the activator metals is impregnationof the support with a solution containing one or more decomposablecompound of the desired metal(s) followed by calcination. Illustrativeof the decomposable compounds which can be used are: copper nitrate,copper acetate, copper acetylacetonate, nickel nitrate, nickelcarbonate, nickel acetate, nickel acetylacetonate, manganese nitrate,manganese acetate, manganese acetylacetonate, manganese carbonate,manganese carbonyl, cobalt nitrate, cobalt acetate, cobaltacetylacetonate, cobalt carbonate, chloroplatinic acid, platinumtetrachloride, palladic acid, palladium chloride, and palladium nitrate.

Various impregnation techniques can be used including dip, evaporativeand vacuum impregnation. One preferred method of impregnation involvesthe use of a steam-jacketed rotary evaporator. The desired support isimmersed in an impregnating solution containing the desired metal(s) inthe drier and the support is tumbled therein by the rotary motion of thedrier. Evaporation of the solution in contact with the tumbling supportis expedited by applying the steam to the drier jacket. The resultantcatalytic composite is dried and then calcined.

In one embodiment of the invention, a microspherical catalytic compositeis used. The microspherical catalytic composite has several advantagesover previously disclosed catalysts. It is well known that a portion ofthe acetylenes present in the hydrocarbon stream will tend to polymerizeand form high molecular weight undesirable byproducts, see, Sarkany, A.;Weiss, A. H.; Szilagyi, T.; Sandor P.; Guczi L. Applied Catalysis 1984,12, 373-379. Furthermore, much of the polymerization occurs within thepores of the catalytic composite with the polymerized products remainingtrapped within the pores and decreasing the activity of the catalyst. Asthe activity of the catalyst declines, the selective nature of thehydrogenation lessens and the amount of hydrogenation of butadienerelative to the amount of hydrogenation of acetylenes is increased.Through using a microspherical catalytic composite, the residence timeof the acetylene within the catalyst before being hydrogenated isreduced thereby decreasing the opportunity for the acetylene topolymerize. In other words, the diffusion path length of the acetylenethrough the composite is reduced allowing for more rapid hydrogenationand less acetylene is available for polymerization. Reducing the amountof acetylene polymerization results in increased catalytic compositestability and enhanced selectivity as demonstrated in the Examples. Withincreased stability, the catalyst may be operated at less severeconditions for a longer period of time with fewer periodic regenerationcycles and no loss of acetylene conversion. In addition, the producteffluent is of higher purity and requires less intense downstreampurification processing. Larger diameter catalysts are expected toprovide the same advantages as discussed above when at least 50 andpreferably 70 weight percent of the copper metal and the activatormetals are dispersed on the outer 200 microns of the catalyst support.

In a preferred embodiment, the copper and the activator metals may beincorporated on the catalytic support using the aforementionedevaporative impregnation technique, where at least 50 weight percent ofthe metals are located in the outer 200 micron layer of the support,preferably where at least 70 weight percent of the metals are located inthe outer 200 micron layer of the support, and more preferably where atleast 80 weight percent of the metals are located in the outer 200micron layer of the support. It is most preferred that at least 88weight percent of the metals are located on the outer 200 micron layerof the support. “Layer” is meant to describe a stratum of substantiallyuniform thickness, and “outer” is meant to define the exterior layer ofthe support. In general terms, surface impregnation can be carried outusing metal complexes that have a high affinity for the support surfaceor complexes which are bulky in nature. It can also be achieved by sprayimpregnation techniques in which the volume of the impregnating solutionis less than that required to fill the pore volume. Techniques forsurface impregnation are known in the art and are described in U.S. Pat.No. 3,259,454, U.S. Pat. No. 3,259,589, U.S. Pat. No. 3,388,077, Lee,S.; Aris, R. Catal. Rev.-Sci. Eng. 1985, 27(2), 207-340; Komiyama, M.Catal. Rev.-Sci. Eng. 1985, 27(2), 341-372; and Dougherty, R. C.;Verykios, X. E. Catal. Rev.-Sci. Eng. 1987, 29(1), 101-150.

Selective hydrogenation of the acetylenes is carried out by contactingthe hydrocarbons with the above-described catalytic composite in a fixedbed system. The hydrocarbon may be preheated to the processingtemperature and hydrogen is admixed. Alternatively, the hydrocarbon andhydrogen may be mixed before preheating the mixture to the processtemperature. This reactant mixture is passed to the fixed bed systemwhich may be a single bed, or multiple sub-beds with heating meanssituated between the individual beds to maintain the reactants at thedesired temperature. The fixed bed system may also be operated in aswing bed mode, with one sub-bed on-line and receiving the reactantmixture while another sub-bed is off-line. The catalytic compositecontaining in the sub-bed off-line may be in the process of beingregenerated, or may have completed regeneration and is ready for use. Asthe reactant mixture contacts the catalytic composite, the acetylenesare hydrogenated leaving the effluent stream essentially acetylene-free.Examples of the selective hydrogenation reactions include hydrogenatingvinyl acetylene to form 1,3-butadiene, hydrogenating ethyl acetylene toform 1-butene, and hydrogenating methyl acetylene to form propylene. Theamount of residual acetylenes expected in the reactor effluent istypically less than 15 wt-ppm. Conditions for the selectivehydrogenation of C₄-acetylenes include a temperature in the range ofabout 20° C. to about 80° C., pressures in the range of from about 15bars to about 50 bars and liquid hourly space velocities in the range offrom about 0.5 to about 10. Hydrogen is also added at a hydrogen toacetylene ratio of from about 1.0 to about 5.0.

The following example is presented as an illustration of one specificembodiment of this invention and is not intended as undue limitations ofthe generally broad scope of the intention as set forth in the claims.The specific embodiment involves a process for selectively hydrogenatingC4-acetylenes in a liquid hydrocarbon stream containing largelybutadiene comprising contacting hydrogen and the hydrocarbon stream witha catalytic composite which is an inorganic oxide support havingdispersed thereon finely divided copper metal and optionally anactivator metal selected from the group consisting of nickel, cobalt,platinum, palladium, manganese, and a combination thereof where thecatalytic composite is spherical and has an average diameter of up toabout {fraction (1/32)} inch (800 microns).

EXAMPLE 1

Alumina spheres were prepared by the well known oil drop method whichinvolves forming an aluminum hydrosol by dissolving aluminum inhydrochloric acid. To this hydrosol, where was added hexamethylenetetraamine to gel the mixture into spheres when dispersed into dropletsinto an oil bath maintained at about 93° C. The droplets remained in theoil bath until they set and formed hydrogel spheres. After the sphereswere removed from the hot oil, they were pressure aged at 130° C. andwashed with dilute ammonium hydroxide solution, dried to 260° C. andcalcined at 640° C. for about 1.5 hours to give gamma alumina sphereshaving an average diameter of {fraction (1/16)} inch (1600 microns).

The metal incorporation was performed using the evaporative impregnationtechnique. First, the impregnation solution was prepared by dissolvingcopper nitrate, nickel nitrate, cobalt nitrate, and manganese nitrate inwater. The resultant solution was then added to a rotary evaporatorloaded with the gamma alumina spheres. After cold rolling the mixturefor 1 hour steam was introduced to the outer jacket to evaporate theexcess water. The metal impregnated catalyst was dried at 210° C. for 1hour and calcined at 400° C. for 2 hours. The above process was repeatedthree times to give three reference catalysts having {fraction (1/16)}inch diameter spheres, identified as Reference 1, Reference 2, andReference 3.

EXAMPLE 2

Again, alumina spheres were prepared by the well known oil drop method.involving forming an aluminum hydrosol by dissolving aluminum inhydrochloric acid. To this hydrosol, where was added hexamethylenetetraamine to gel the mixture into spheres when dispersed into dropletsinto an oil bath maintained at about 93° C. The droplets remained in theoil bath until they set and formed hydrogel microspheres, After themicrospheres were removed from the hot oil, they were pressure aged at120° C. and washed with dilute ammonium hydroxide solution, dried at205° C. and calcined at 640° C. for about 1.5 hours to give gammaalumina microspheres having an average diameter of {fraction (1/32)}inch (800 microns).

The metal incorporation was performed using the evaporative impregnationtechnique. First, the impregnation solution was prepared by dissolvingcopper nitrate, nickel nitrate, cobalt nitrate, and manganese nitrate inwater. The resultant solution was then added to a rotary evaporatorloaded with the gamma alumina spheres. After cold rolling the mixturefor 1 hour steam was introduced to the outer jacket to evaporate theexcess water. The metal impregnated catalyst was dried at 210° C. for 1hour and calcined at 400° C. for 2 hours.

The microspherical catalyst was analyzed and compared to the referencecatalysts prepared in Example 1. Table 1 shows the results of themicrospherical catalyst analysis as compared to the typical result forthe three reference catalysts with all concentration units in weightpercent of the catalytic composite.

TABLE 1 1/32 inch 1/16 inch copper, wt. % 7.1 7.6 nickel, wt. % 0.2 0.19cobalt, wt. % 0.10 0.10 manganese, wt. % 0.15 0.14 average bulk densityin g/cc 0.73 0.80 BET surface area, m²/g 179 182

EXAMPLE 3

The catalysts prepared in Examples 1 and 2 were evaluated in a selectivehydrogenation process with the results demonstrating the enhancedstability and selectivity of the microspherical catalyst of Example 2 ascompared to Reference catalysts 1, 2, and 3 of Example 1. A reactor wasloaded with 16 g of the microspherical catalyst prepared in Example 2and heated to an inlet temperature of 60° C. A crude C₄ hydrocarbonstream from a naphtha cracker complex and containing about 38 wt. %1,3-butadiene and 0.35 weight percent of vinyl. acetylene and 0.13 wt. %ethylacetylene was introduced to the reactor at an acetylene weighthourly space velocity of 0.15. The hydrogen to acetylene molar ratio was2.1. The effluent was analyzed by gas chromatography and the resultingdata is provided in FIGS. 1-6. The experiment was repeated three moretimes at the same conditions to test Reference catalysts 1, 2, and 3 ofExample 1. To test Reference catalyst 1, the reactor was loaded with 16g of Reference catalyst 1 prepared in Example 1. To test Referencecatalyst 2, the reactor as loaded with 16 g of Reference catalyst 2prepared in Example 1. To test Reference catalyst 3, the reactor wasloaded with 16 g of Reference catalyst 3 prepared in Example 1. Theresults of all analyses are provided in FIGS. 1-6.

FIG. 1 shows the weight percent conversion of vinyl acetylene thatoccurred over time during each of the experiments. The data clearlyshows the increased stability of the microspherical catalyst over timeas compared to the reference catalysts. The microspherical catalyst ofExample 2 remained at greater than 90 weight percent conversion of vinylacetylene for 70 hours on stream, while the reference catalysts ofExample 1 showed less than 80 weight percent conversion at 70 hours onstream. Similarly, FIG. 2 shows the microspherical catalyst of Example 2remained at greater than about 78 weight percent conversion of totalacetylenes at 70 hours on stream, while the reference catalysts ofExample 1 showed less than about 75 weight percent conversion totalacetylenes at 70 hours on stream. The enhanced selectivity of themicrospherical catalyst is demonstrated in FIG. 3 which shows higherbutadiene retention (weight percent of butadiene in the effluent dividedby weight percent butadiene in the feed) with the microsphericalcatalyst; in FIG. 4 which shows overall less hydrogen conversion whenusing the microspherical catalyst; and in FIG. 5 which shows lowerhydrogen to acetylene usage ratio indicating that less hydrogen is beingconsumed through hydrogenation of butadiene when using themicrospherical catalyst. FIG. 6 indicates that the selectivity forpolymeric byproducts, or green oil, is less when using themicrospherical catalyst of Example 1.

What is claimed is:
 1. A process for selectively hydrogenatingC4-acetylenes in a liquid hydrocarbon stream containing largelybutadiene comprising contacting hydrogen and the hydrocarbon stream witha catalytic composite comprising an inorganic oxide support havingdispersed thereon finely divided copper metal and an activator metalselected from the group consisting of nickel, cobalt, platinum,palladium, manganese, and a combination thereof said catalytic compositehaving an average effective diameter of about {fraction (1/32)} inch(800 microns) wherein at least 70 weight percent of said copper metaland said activator metal are dispersed on the outer 200 microns layer ofthe support.
 2. The process of claim 1 wherein the catalytic compositeis of a shape selected from the group consisting of a sphere and anextrudate.
 3. The process of claim 1 wherein at least 80 weight percentof said copper metal and said activator metal ed on the outer 200 micronlayer of the support.
 4. The process of claim 1 wherein the inorganicoxide support is selected from the group consisting of alumina, silica,magnesia, zirconia, and titania.
 5. The process of claim 1 wherein theC4-acetylenes include ethylacetylene, methylacetylene andvinylacetylene.
 6. The process of claim 1 wherein the selectivehydrogenation conditions include a temperature of about 20° C. to about80° C., a pressure of from about 15 bars to about 50 bars, a liquidhourly space velocity of from about 0.5 to about 10, and a hydrogen toacetylene ratio of about 1.0 to 5.0.
 7. The process of claim 1 whereinsaid copper metal is present in an amount ranging from about 5 to about15 weight percent of the catalytic composite.
 8. The process of claim 1wherein said activator metal is present in an amount ranging of fromabout 0.1 to about 1 weight percent of the catalytic composite.